Laser-guided munitions (generally referred to as laser-guided bombs (LGBs), laser guided weapon systems (such as in an aircraft), or laser-guided weapons (LGWs) use a laser designator to mark (illuminate, “paint”) a target. The reflected laser light (“sparkle”) from the target is then detected by the seeker head of the weapon, which sends signals to the weapon's control surfaces (e.g., fins) to guide the weapon toward the designated point. The illuminating laser light is encoded, and the laser receiver in the LGW is set to react only to reflected laser light having the proper code.
FIG. 1 illustrates an exemplary procedure for aircraft with laser-guided weapons (LGWs) and laser spot trackers, as set forth in Joint Pub 3-09.1, Joint Tactics, Techniques, and Procedures for Laser Designation Operations, 28 May 1999, incorporated in its entirety by reference herein.
In this scenario 1, an aircraft 2 is equipped with a LGW 3 which is shown already in its ballistic trajectory towards a target 5. Also illustrated is a forward air controller (FAC), and a laser designator operator (LDO). The FAC is in radio communication with the pilot of the aircraft 2 and with the LDO. The LDO illuminates the target 3 with a laser, and laser light is reflected back, typically as scattered reflections called “sparkle”.
Generally, the sequence of events is that the maneuver unit commander (not shown) decides to request close air support. The FAC coordinates laser code, laser target line and frequency and/or call sign of the LDO. The airstrike request includes laser-related data. An airstrike approval message is received, and the aircraft is dispatched to a contact point to check in with FAC. The FAC coordinates laser code, laser-target line and frequency and/or call sign with LDO and pilot. Approaching the target, the aircraft calls in. The FAC relays laser control calls. The LDO designates the target (by illuminating it with laser beam). The aircraft acquires the target or releases the LGW. The LGW heads towards the target, adjusting its trajectory based on sparkle from the laser-illuminated target. The target is destroyed.
Laser designators and seekers may use a pulse coding system to ensure that a specific seeker and designator combination work in harmony. Setting the same code in both the designator and the seeker enables the seeker to track only laser beams with the correct coding. The seeker may track the first correctly coded, significant laser energy it sees. The seeker may lock on to the most powerful return in its gate; choose the last pulse, or a selected logic. The pulse coding is usually based on pulse repetition frequency (PRF), but may be based on PIM (Pulse Interval Modulation) coding.
In the prior art, many techniques have been devised to improve the accuracy of the identification of the target by the seeker head of LGWs.
U.S. Pat. No. 5,350,134, incorporated in its entirety by reference herein, discloses target identification systems. A target identification system includes a target marker for selecting, and directing radiation at, a target, a weapon delivery system, and means for establishing a two-way communication channel between the two by reflection from a selected target. The communication is by infra-red laser and coded information is sent between the target marker and the weapon delivery system to identify the selected target.
U.S. Pat. No. 7,575,191 uses an engineered diffuser to generate a preferred square pattern on to a quadrant detector. The abstract, text and every claim describes a detector with at least two axes. U.S. Pat. No. 8,164,037 describes a dual mode SAL. FIG. 3A shows the traditional quadrant detector. U.S. Pat. No. 8,188,411 teaches a immersed filter stack and field lens. FIG. 3A shows the quadrant detector equations. U.S. Pat. No. 8,207,481 shows the use of a Fresnel lens with a sharp step used as an objective element. FIG. 2A shows the quadrant detector equations. U.S. Pat. No. 8,541,724 describes a smart weapon. Column 11 line 49 on describes the quadrant seeker. The use of a single defocused spot (see commonly-owned U.S. Pat. No. 8,451,432) is discussed in column 12. Commonly-owned application Ser. No. 14/672,149 shows a method of homogenizing the spot based on a dual focus lens.
Laser designation and spot tracking is well known and is described in commonly-owned U.S. Pat. No. 7,773,202 issued 10 Aug. 2010, U.S. Pat. No. 8,451,432 issued 28 May 2013, and U.S. 61/971,651 filed 28 Mar. 2014